Conventionally, as this kind of control apparatus, there is an apparatus which includes a transistor chopper-type exciting circuit that supplies an exciting current for a vehicle from a generator, and in which a current for exciting a rotor is regenerated in a battery (see PTL 1). In the apparatus disclosed in PTL 1, on condition that a key switch of an engine is in an off state, and rotation speed of the engine is equal to or lower than 200 rpm, a power transistor connected on an earth side is put into an ON state, and a power transistor connected on an output terminal side is put into an OFF state at the above-described exciting circuit. Accordingly, an exciting winding of the rotor is prevented from having a floating potential when an engine is not operated after traveling to prevent or suppress corrosion of the rotor due to a leakage current.